The conventionally known drug administration methods include oral administration methods using tablets, capsules, syrup, etc., and attempts have been made in recent years to administrate the drugs through skin by use of patch agents. Since the administration method using the patch agents has the advantages of decrease in the number of administration times, improvement in compliance, easiness of administration and discontinuation thereof, etc., in addition to solving problems in the oral administration methods, it is thus expected to be a drug administration method useful, particularly, in treatments of elderly and child patients.
Incidentally, the corneum of normal skin has a barrier function of preventing foreign matter from getting into the body, and it is thus often the case that the base used in the ordinary patch agents fails to achieve satisfactory transdermal absorption of a medicinal component blended therein. In addition, the corneum is highly fat-soluble, and thus the drugs demonstrate extremely low permeability in general. For this reason, it becomes necessary to enhance the transdermal absorbability of the drug through the corneum of skin, for administering the drug through skin by use of the patch agent.
Research thus has been conducted heretofore to implement optimization of the composition of an absorption promoter including various transdermal absorption promoting agents, and an adhesive component. Particularly, concerning the adhesive base of the patch agent, it is important to design the adhesive base so as to blend various (adhesive) polymers and provide it with satisfactory preparation properties and optimal drug solubility, and from this point of view, polymer materials such as acrylic polymers, rubber-based polymers, silicone-based polymers, or the like are generally used as pressure-sensitive adhesive bases.
These polymer materials demonstrate different features as to the transdermal absorbability of the drug. For example, the rubber-based polymers with relatively low solubility of the drug have high transdermal absorbability of the drug but have a limitation to amounts of the drug that can be included; therefore, drug absorption rates are likely to drop during application of the patch agent, so that the level of the drug in the blood decreases, so as to fail to achieve continuous effect (Journal of New Remedies & Clinics, 48, 1015-1-24, 1999). The rubber-based polymers have low solubility of the drug and readily cause crystallization of the drug in the preparation with a lapse of time, so as to fail to achieve satisfactory stability in certain cases.
The acrylic polymers demonstrate higher solubility of the drug but lower absorption of the drug than the rubber-based polymers. For this reason, the concentration of the drug needs to be increased in order to achieve necessary absorption of the drug in the patch agents using the acrylic polymers, and this can cause failure in achieving satisfactory preparation properties in formulation, or increase the cost.
In order to avoid the phenomena occurring in the cases using the above polymers, proposals were thus made on methods using the adhesive base containing a blend of polymers.
For example, National Publication of Translated Version of PCT Application, Publication No. H04-502719 discloses pressure-sensitive adhesive dermal compositions containing a blend of a polymer mixture of a vinyl acetate/ethylene copolymer and an acrylic polymer, a natural or synthetic rubber, and a tackifier. In addition, National Publication of Translated Version of PCT Application, Publication No. H09-511987 discloses pressure-sensitive adhesive compositions containing a polyacrylate, a rubber, a drug, and a soluble polyvinylpyrrolidone.